Make zookeeper healthchecks compatible with Alpine's busybox nc

[lhotari]

Motivation

The apachepulsar/pulsar:3.3.0 image contains busybox nc which doesn't support -q 1 command line option.
See apache/pulsar#22872.

Modifications

• replace -q 1 with the use of sleep 1 in the input.
  • Solution from https://unix.stackexchange.com/a/274603.
• replace "localhost" with "127.0.0.1" (so that IPv4 gets selected?)

Verifying this change

• Make sure that the change passes the CI checks.

[lhotari]

There's some other issue with the Alpine image:

Server:        10.96.0.10
Address:    10.96.0.10:53

** server can't find pulsar-ci-zookeeper-0.pulsar-ci-zookeeper.pulsar: NXDOMAIN

** server can't find pulsar-ci-zookeeper-0.pulsar-ci-zookeeper.pulsar: NXDOMAIN

/etc/resolv.conf is

search pulsar.svc.cluster.local svc.cluster.local cluster.local 1evhaya2a4vu1idbbq22av5vmh.bx.internal.cloudapp.net
nameserver 10.96.0.10
options ndots:5

[lhotari]

Some DNS config issue:

pulsar-ci-pulsar-init-pfdv8:/pulsar$ nslookup pulsar-ci-zookeeper-0.pulsar-ci-zookeeper.pulsar.svc.cluster.local
Server:         10.96.0.10
Address:        10.96.0.10:53

Name:   pulsar-ci-zookeeper-0.pulsar-ci-zookeeper.pulsar.svc.cluster.local
Address: 10.244.1.17


pulsar-ci-pulsar-init-pfdv8:/pulsar$ nslookup pulsar-ci-zookeeper-0.pulsar-ci-zookeeper.pulsar
Server:         10.96.0.10
Address:        10.96.0.10:53

** server can't find pulsar-ci-zookeeper-0.pulsar-ci-zookeeper.pulsar: NXDOMAIN

** server can't find pulsar-ci-zookeeper-0.pulsar-ci-zookeeper.pulsar: NXDOMAIN

[lhotari]

found k3s-io/k3s#6561 (comment) , but not a proper resolution.

[lhotari]

Looks like busybox nslookup isn't compatible. docker-library/busybox#48 (comment)

will need apk add bind-tools in Alpine image.